Conventionally, the uniformity of a semiconductor device is achieved by processes of masking and etching or by a process of polishing with a chemical-mechanical polishing machine. Preference is given to the process of polishing with a chemical-mechanical polishing (CMP) machine. The process of polishing by chemical-mechanical polishing essentially comprises the steps of holding the semiconductor device by holding means and polishing with a spinning polishing pad, to get rid of the an excess portion of the semiconductor device or to get a uniform thickness for the semiconductor device. In order to enhance the efficacy of polishing, a polishing slurry must be continuously added to the polishing pad. Additionally, during the period of being not used, deionizing water must be added so as to maintain the wetness of the polishing pad and to facilitate the proceeding of further polishing. Conventionally, the used polishing slurry and deionizing water are collected and drained out to a waste liquid storage tank. Nowadays, the process of chemical mechanical polishing is used more frequently, and accordingly, the amount of the used polishing slurry and deionizing water is getting greater. Further, the cost of the polishing slurry and deionizing water per se and the treatment of the used polishing slurry and deionizing water are relatively high, thus the recovery and re-use of the used polishing slurry and deionizing water is more important than ever.